Place the oil in a large pot set over medium to medium-high heat. Add the next 5 ingredients and cook until softened, about 4 to 5 minutes. Mix in the flour and cook 2 minutes more. While stirring, slowly mix in the stock. Mix in the sage, paprika and nutmeg. Bring the soup to a slow simmer and cook until the vegetables are quite tender, about 20 minutes. Puree the soup in a blender or food processor, or in the pot with an immersion blender. Return soup to a simmer; thin with a bit more stock if you find it too thick. Season the soup with salt and pepper. Ladle the soup into heated bowls. Divide and top each soup with cheese and nuts and serve.
Note: To toast walnuts, set them in a non-stick pan over medium heat. Heat them few minutes, until fragrant and lightly toasted.